Electric power is often generated in a thermal power station having closed cycle with water as work medium. Due to various reasons, the water leaves the cycle, and it should be substituted by very clean water/ of approximately 0.1 .mu.S/cm conductivity/. The clean water is to be produced from a much more contaminated water /hereinafter raw water/ to be found in the vicinity of the power station. This operation is called the making up of feed water for the power station.
Earlier, the distillate for making up feed water was produced in the form of steam by an evaporator device matched to the system of the power station. The evaporator device was e.g. connected between two bleedings of the steam turbine. Nowadays, the production of the make-up water of the required purity is mostly based on a so-called complete desalination equipment consisting of ion exchange devices, cation and anion exchanging columns.
The application of evaporator devices was uneconomical in most cases because they were either of simple operation with a high steam consumption, or of multi-body type, in the latter case their start-up and stopping entailed problems, since it was possible in a longer period only, and resulted in a huge steam loss, as well as in a regulation requirement, causing serious difficulties in the operation of the power station.
There are equipments based on ion exchange for producing make-up water. They have a double disadvantage: on the one hand, the chemicals are costly, and on the other hand, due to regeneration, chemicals are introduced into the environment, mostly into live waters. The quantity of contaminating materials introduced in the environment increases together with the contamination of the raw water. Since the available raw waters are increasingly contaminated, the chemical consumption also increases, and the entailed environment pollution is starting to be unbearable today. Therefore, the environment protection and the costs of chemicals dramatically increase the costs of ion exchange processes.
Equipment based on reverse osmosis has already been suggested for producing make-up water. However, the purity of water supplied by reverse osmosis is not satisfactory for power station purposes, so it is inevitable to use an ion exchange device after this unit. On the other hand, the energy required for driving the reverse osmosis devices should be supplied in the form of mechanical energy, therefore in the case of power station start-up, its availability under any condition should be ensured by diesel power generator or a co-operation network.